Don't upgrade to CUCM 12 without a lot of planning. Among other things, the licensing model has completely changed and you don't want to go there until you are ready.
As Jaime pointed out, I was reading from the PDF for 11.5(1) I downloaded last year. The current online documentation says that 11.5(1) is compatible with AD 2012-R1/R2 and MLDS 2012-R1/R2 so that is not the answer after all. I don't know what the problem is, though.
I disagree with you on the cucm 12 upgrade complexity. I found it pretty straight forward. Yes licensing has changed but IMO it's more simple in 12. To get to 12, you just export the license request from PLM and send it to the Cisco licensing team to convert your licenses and add them to your cisco.com smart account. Then you upgrade CUCM. When you log in to CUCM you then use the gui to register the CUCM pub with the smart account and the licenses are sync. Not really much more to it than that.
Must of course read the upgrade guide. There is not much thorough info there about the licenses, it doesnt tell your exactly what to do. So to save any confusion on my part I just emailed the licensing team with my intent and the license request file.
Not Solved. New wrinkle.
I found a post at https://www.cisco.com/c/en/us/support/docs/unified-communications/unity-connection/117737-problem-uc-00.html which directed a look at the database tables. I found the entry of the user I have been trying to import in the table 'u' with a pkid assigned and the info from 'active directory'. But I didn't find any other entries in the tables listed in the URL above.
It appears Unity is reading the ldap directory just fine but will not finish the import.
I have rebooted the server with no effect.
Still trying to solve.